Typically, when a remote node 152 uses a service provider to establish a remote connection with a separate network, the remote node 152 will dial into the service provider's local Network Access Server (NAS) 154. As shown in FIG. 1, the NAS 154 usually includes several port interfaces. Each remote node dials into the NAS 154 through a separate port interface. Data received through interfaces may in turn be multiplexed over one synchronized line 156 providing a connection to a Wide Area Network (WAN) access device 260.
The data is usually transmitted between the remote nodes and the NAS 154 over an asynchronous line (e.g. telephone line). Therefore, the NAS typically needs to frame the packets of data received from the remote node into data-link control protocol frames (e.g. High-level Data Link Control (HDLC)) in order to transmit the packets over the synchronous line 156. (References herein to the data-link layer and the network layer are references to the Open Systems Interconnection (OSI) model developed by the International Standardization Organization).
As shown in FIG. 1, the synchronous line 156 between the NAS 154 and the WAN access device 160 is usually a point-to-point connection. That is, a connection with out any intervening nodes or switches.
As a result of the point-to-point nature of the connection, the address field of the data-link frame is not used because the frame has only one possible destination once it is transmitted. Usually, the address field of a data-link frame is used to indicate the physical destination of the frame so that any switches between a frame's source and destination will be able to read the frame's address field and know where to forward the frame. However, when it is known that there will be no intervening switches between the frame's source and destination (e.g. point-to-point connection) no address is necessary. In fact, the RFC 1662 states that for point-to-point connections, the address field of the HDLC frame should contain 0.times.FF.
When the NAS 154 receives responses from the WAN access device 160, the NAS 154 usually performs a routing function to determine where the response is to be forwarded. That is, the NAS 154 will strip the response packet from its data-link frame and read the packet's address information, which is usually provided at the network layer (e.g. the Internet Protocol (IP) address). The routing procedures, however, slow down the transmission of the responses and usually only work if the node to which a response is being delivered, has been given a network address.
In the case of a user dialing into a NAS 154 from a unit that does not have a network address (e.g. a terminal), the NAS will usually assign a network address to each packet received from that unit. The assigned network addresses will in turn will be used by the NAS to forward responses using the routing procedures described above. Assigning network addresses, however, has the disadvantage of preallocating several network addresses, when in fact, some of these addresses may not be used.
Therefore, what is needed is a way for an access server to forward data-link frames received from a point-to-point connection without having to perform routing operations.